Linkpreviewer Improvements

- Have LinkPreviewers stored in NeoChatConnection so that they don't have to be reloaded everytime the MessageContentModel is refreshed
- This means the link is never changed (it will be swiched for a new previewer with the new link)
- LinkPreviewers are stored by URL so they can be re-used by any event with the same URL

BUG: 484927  (because the offending code is ripped out)

src/neochatconnection.h

@@ -9,6 +9,8 @@
 #include <QCoroTask>
 #include <Quotient/connection.h>
 
+class LinkPreviewer;
+
 class NeoChatConnection : public Quotient::Connection
 {
     Q_OBJECT
@@ -147,6 +149,8 @@ public:
 
     bool isOnline() const;
 
+    LinkPreviewer *previewerForLink(const QUrl &link);
+
 Q_SIGNALS:
     void labelChanged();
     void directChatNotificationsChanged();
@@ -166,4 +170,6 @@ private:
     void connectSignals();
 
     int m_badgeNotificationCount = 0;
+
+    QHash<QUrl, LinkPreviewer *> m_linkPreviewers;
 };